Calculation Of Aortic Valve Area

The peak gradient across the aortic valve is calculated using the modified Bernoulli equation


Peak gradient = 4 x (peak velocity)²

where v is the peak velocity of flow across AV. However, when the peak velocity is < 2.0 m/s,

this equation cannot apply, and a longer version of the Bernoulli equation should be used.

The velocity should be measured at the LVOT (V1) and the aortic valve (V2).

The peak gradient is

Peak gradient = 4 x (V2² - V1²)

The effective orifice area is calculated using the continuity equation. The principle of the continuity equation is that the amount of blood pumped out of the left ventricle through the left ventricular outflow tract (LVOT) in 1 second should be equal to the volume of blood passing through the aortic valve in 1 second.

Calculating the effective orifice area (EOA) requires certain preliminary measurements.

These include

• LVOT diameter
• LVOT vti on pulse wave doppler
• LVOT area
• Aortic valve (AV) vti on continuous wave doppler

First, the LVOT area is calculated using the formula

LVOT area = 𝝿 x (LVOT diameter/2)²

where 𝝿 = 3.14.

The EOA is calculated as follows

  EOA = (LVOT area x LVOT vti) / AV vti

The continuity equation is useful when there is coexistent aortic regurgitation (regardless of severity)
and left ventricular dysfunction.